1. Field of the Invention
This invention relates to a class of compounds of hexavalent sulfur referred to as sulfonimidates. More particularly, this invention relates to a group of novel sulfonimidates wherein the carbon atom bonded to sulfur is other than a cyclic carbon atom of an aromatic hydrocarbon radical. This invention also relates to a method for preparing both the novel sulfonimidates of this invention and prior art sulfonimidates using the corresponding N-triorganosilyl sulfonimidate as a precursor. Some of the sulfonimidates can be converted to useful thermally stable and solvent resistant polymers referred to as polyorganooxothiazenes.
2. Description of the Prior Art
Levchenko et al. in Zh. Obsch. Khim. 32, 2585 (1962) describe the preparation of phenyl esters of areneiminosulfonic acids represented by the general formula ArS(O)(.dbd.NH)OC.sub.6 H.sub.5 where Ar represents a phenyl radical. Esters of iminosulfonic acids have also been referred to as sulfonimidates. Levchenko et al. also report that heating one of the esters they prepared yielded a tarry material that was characterized only by a softening temperature of 80.degree. to 100.degree. C.
Carl Johnson in the Journal of Organic Chemistry, 44, 13 (2055-2061), published on Jun. 22, 1979, reports obtaining a polymer from the reaction of a sulfonimidoyl chloride corresponding to the formula PhSCl(O).dbd.NH, where Ph represents a phenyl radical, with pyridine, methylamine or dimethylamine. The article does not describe the isolation of the polymer nor does it provide any structural or other characterization data obtained from the polymer.
The compounds used to prepare the polymers reported in the aforementioned articles by Levchenko et al. and Johnson were, in turn, synthesized from compounds wherein sulfur is in the tetravalent state. Many tetravalent sulfur compounds used in the synthesis of sulfonimidates suffer from one or more of the following disadvantages: they are difficult to synthesize and/or purify, are not readily accessible or available, malodorous, and have limited shelf life due to decomposition during long-term storage. In addition, some of the reactants used to convert the sulfur in these compounds from the tetravalent to the hexavalent state suffer from some of the same disadvantages as the compounds they are intended to convert. Moreover, some of these reactants are high energy compounds, and potentially explosive.
U.S. patent application Ser. No. 07/644,761, filed in the name of the present inventor and Gary Burns on Jan. 23, 1991 teaches the preparation of N-triorganosilylsulfonimidates from hexavalent sulfur compounds such as sulfonic acids and their derivatives, including the chlorides, anhydrides and amides. Most of the final compounds and intermediates are generally very stable, readily available, and can be handled in large quantities without exercising more than the ordinary precautions involved in handling acidic and corrosive materials.
Heating the silylated sulfonimidates converts them to polyorganooxothiazenes containing repeating units represented by the general formula --N.dbd.S(O)(R.sup.1)--, where R.sup.1 represents an unsubstituted or substituted hydrocarbon radical. This thermally induced condensation reaction requires prolonged heating, typically at temperatures in the range from 100.degree. to 160.degree. C. for periods of about 140 hours, sometimes in the presence of a polymerization catalyst. The yields of polymer reported in the examples of the patent application range from 39 to 83 percent, with only one instance of a 97 percent yield using a tungsten compound as the catalyst.
One objective of this invention is to provide precursors, some of which are novel, that will yield polyorganooxothiazenes in higher yield using lower temperatures and shorter polymerization times than reported in the aforementioned patent application.